How can we create a custom immutable class in Java?

How can we create immutable class if there is some mutable object in class?

If you want to encapsulate a mutable object into an immutable one, then you need to:

1. Create a copy of the mutable object (i.e. via copy constructor, cloning, serialization/deserialization, etc.); never store the reference to the original mutable object.
2. If you must to, then return a copy of the object.

How do you make a class mutable in Java?

Declare the class as final so it can’t be extended. Make all fields private so that direct access is not allowed. Do not provide setter methods (methods that modify fields) for variables, so that it can not be set. Make all mutable fields final so that their values can be assigned only once.

How can we make an object immutable in Java?

To make object immutable, You must do these steps:

1. Don’t use any methods, which can change fields of your class. For example don’t use Setters.
2. Avoid to use public non-final fields. If your fields is public then you must declare them as final and initialize them in constructor or directly in the declaration line.

Why do we create immutable class in Java?

Immutable objects are thread-safe so you will not have any synchronization issues. Immutable objects are good Map keys and Set elements, since these typically do not change once created. Immutability makes it easier to parallelize your program as there are no conflicts among objects.

How can we make an immutable class employee in Java?

To create an immutable class in Java, you have to do the following steps.

1. Declare the class as final so it can’t be extended.
2. Make all fields private so that direct access is not allowed.
3. Don’t provide setter methods for variables.
4. Make all mutable fields final so that its value can be assigned only once.

What if immutable class contains mutable object in Java?

Immutable class is a class which once created, it’s content can not be changed. Immutable classes are good choice for HashMap key as their state cannot be changed once they are created.

How can we make a class mutable?

The essentials for creating a mutable class are methods for modifying fields, getters and setters. The essentials for creating an immutable class are final class, private fields, final mutable objects.

How can we create singleton class in Java?

To create the singleton class, we need to have static member of class, private constructor and static factory method.

1. Static member: It gets memory only once because of static, itcontains the instance of the Singleton class.
2. Private constructor: It will prevent to instantiate the Singleton class from outside the class.

What is a mutable class in Java?

Mutable objects are objects in which we can make changes to an object’s state without creating a new object. … Examples of mutable classes in java are java. util. Date, StringBuffer, StringBuilder, etc., whereas java legacy classes, wrapper classes, String class are examples of immutable classes in java.

How can you make an object immutable?

To create an immutable object you need to follow some simple rules:

1. Don’t add any setter method. …
2. Declare all fields final and private. …
3. If a field is a mutable object create defensive copies of it for getter methods. …
4. If a mutable object passed to the constructor must be assigned to a field create a defensive copy of it.

What is mutable and immutable in Java?

A mutable object can be changed after it’s created, and an immutable object can’t. Strings are immutable in Java. …

What is Java object immutability?

An object is considered immutable if its state cannot change after it is constructed. … Immutable objects are particularly useful in concurrent applications. Since they cannot change state, they cannot be corrupted by thread interference or observed in an inconsistent state.

Is immutable thread-safe?

To put it simply, a class instance is immutable when its internal state can’t be modified after it has been constructed. A MessageService object is effectively immutable since its state can’t change after its construction. Hence, it’s thread-safe.

Why wrapper classes in Java are immutable?

The wrapper classes are immutable because it just makes no sense to be mutable. Consider following code: int n = 5; n = 6; Integer N = new Integer(n); At first, it looks straightforward if you can change the value of N, just like you can change the value of n.

Where do we use immutable class in Java?

When to Use Immutable Classes

Modifying immutable state consists of a copying the immutable object. This allows us to read the state without the need of synchronization blocks. So you should use immutable classes when it is feasible to copy the object for every modification and you need read-only access to the data.